The low polarity (hydrophobicity) and inert characteristics of the surface of many thermoplastic and elastomeric polymers, especially polyolefins (PO), cause many problems in the repair, assembly, insertion and coating of these polymers with the same or other materials, especially in structural applications. Hot-melt adhesives are often used, because they are able to penetrate into the polymer surface to create good fusion bonding with the polymeric matrix. To promote the fusion bonding process, heat-gun, hotplate, ultrasonic, vibration, and resistance welding may be applied. Alternatively, surface treatment by plasma, flame, or laser, which allows joining of parts by conventional adhesives, is also sometimes used.
For hot-melt adhesives, heat-gun techniques are not sufficient for joining large areas and it is very difficult to control the uniformity and reproducibility of the joint. In addition, when assembling dissimilar materials, it is not always possible to find an adhesive that provides good bonding with both substrates. In hotplate welding, high temperature is always required for good fusion bonding, and this is not always easy to accomplish for large and/or thin parts with complex shape. Similarly, vibration and ultrasonic welding also present difficulties in joining large parts with complex shapes, and in controlling fibre alignment. Furthermore, especially for PO composites, and especially in structural applications, strong enough adhesion is required to carry the load into/through the joint. Commercial hot-melt adhesives cannot sustain such high load levels while surface treatment techniques are not always practical in industrial applications.
Primers have been used in the past to improve adhesion between two surfaces.
U.S. Pat. No. 6,344,500 issued on Feb. 5, 2002 to Ogawa et al. discloses an aqueous primer coating composition comprising a blend of an acid anhydride-modified poly(olefin chloride) emulsion resin, an aqueous alkyd resin and an aqueous novolac-type epoxy resin for coating a plastic material to impart gasohol resistance.
U.S. Pat. No. 6,337,134 issued on Jan. 8, 2002 to Takai discloses a primer composition for paint comprising a blend of 100 parts by weight of an epoxidized EPDM and 50 to 70 parts by weight of a product of chlorination of a polyolefin modified with an unsaturated carboxylic acid or an anhydride thereof.
U.S. Pat. No. 6,494,983 issued on Dec. 17, 2002 to Graue et al. discloses a cured enamel coating for a metal surface comprising a solids mixture of an epoxy resin, a phenolic resin, carboxy-polyolefin resin and polyester resin.
U.S. Pat. No. 6,497,337 issued Dec. 24, 2002 to Kehe discloses an enamel comprising a blend of a cresol-formaldehyde/epoxy resin and maleic anhydride-modified polypropylene resin adhesion promoter.
U.S. Pat. No. 6,391,461 issued May 21, 2002 to Ryntz et al. discloses a method of improving adhesion to thermoplastic olefins using an adhesion promoter selected from the group consisting of a chlorinated polyolefin, a hydrogenated poly(butadiene)diol, and mixtures thereof.
There remains a need for an effective and easy to use primer for use in the repair, assembly, insertion and/or coating of thermoplastic and/or elastomeric substrates, especially with other dissimilar materials like, for example, thermosets and their composites, thermoplastics and their composites, elastomers, metals, ceramics, wood, leather, fabrics, etc. For example, there remains a need for a primer particularly useful for providing high bond strength in the repair, assembly and/or insertion of thermoplastic and/or elastomeric composites.